Method and apparatus for upsetting steel wires

ABSTRACT

Steel wires or bars headed by conventional methods have generally lacked uniformity in strength having their worked end portions reduced in strength compared with the remaining body portion. It has been found that such reduction in strength can be avoided by selecting appropriate working conditions including heating time and temperature so as to satisfy a relation specific to the material and size of the wire stock.

United States Patent [72] Inventors Chisato Okada [51] Int. Cl.. -B23j 5/08, Tokyo; H05b 1/00 Yoshiaki l-loriuchi, Fujisawa, both of. [50] Field of Search 219/150, Japan 151,152, I54 [2i] Appl. No. 35,047 [22] Filed May 1970 [56] References Cited [45] Patented June 8, 1971 UNITED STATES PATENTS Assignee 83 Cnnmte ay Kabushiki Kaisha 2,665,359 1/1954 Knight 219/3 [32] Priority 2 3 {322 Primary E.raminerJ. V. Truhe [33 1 Japan Assistant Examiner-Lawrence A. Rouse [3 l] 4 78 4 Attorney-Oldham and Oldham Continuation-impart of application Ser. No. 637,515, May 10, 1967, now abandoned.

ABSTRACT: Steel wires or bars headed by conventional methods have generally lacked uniformity in strength having their worked end portions reduced in strength compared with the remaining body portion. lt has been found that such reduc- [54] APPARATUS FOR UPSETTING tion in strength can be avoided by selecting appropriate work- 4 Cl 2 D ing conditions including heating time and temperature so as to satisfy a relation specific to the material and size of the wire [52] U.S.Cl 219/151 stock.

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i METHOD AND APPARATUS FOR UPSETTING STEEL WIRES This application is a continuation-in-part of our now abandoned application Ser. No. 637,5 l5, filed May 10, 1967.

The present invention relates to methods of an apparatus for upsetting the end portions of steel wires, for example, steel tendons for tubular prestressed concrete, to form thereon enlarged heads for anchoring purpose.

It is the object of the present invention to provide an upsetting method which makes it possibleto produce headed steel wires with their head or upset portion having a strength at least comparable with that of their remaining portion and thus advantageously usable in the prestressing of concrete or other intended application in a reduced length of time with simple apparatus and easy operation.

The term steel wires" as used in this specification is intended also to include what are called in practice steel bars.

, Heretofore, for upsetting or enlarging end portions of steel wires, use has generally been made of a so-called header or upsetter-in which the wire end is heated to an elevated temperature and worked under the pressure of the die in the machine to form an enlarged head somewhat like a rivet head.

In the prior art, however, it has been impossible to avoid any reduction in strength of the wire end portion due to its heating, particularly in cases where the wire is of high-carbon steel or heat-treated cold-drawn steel. In fact, it is not infrequent that such steel wire with its upset head is fractured at its neck when subjected to the tension test owing to the reduction in strength of the worked wire portion.

In view of this, the inventor has conducted a large number of experiments with wires of different steel materials and found that what strength is obtained in the upset portion of the wire stock or whether the headed wire when tension tested will be fractured at its neck or at a point on its body portion depends definitely upon the correlation of the heating time and temperature used and that as satisfactory strength can be obtained at the wire neck portion even when it is worked at a considerably high temperature so long as the work is completed with a corresponding reduced heating time.

In the drawing, FIG. 1 illustrates one example of the result obtained with such experiments, and H0. 2 is a schematic illustration of an upsetting apparatus embodying the principles of the invention, particularly showing its pneumatic system and electric circuitry.

In the experiments shown in FIG. 1, specimens were prepared by cold-drawing standard high-manganese high-carbon steeL-including as main ingredients 0.80 percent C and 0.80 percent Mn, at a reduction ratio of approximately 50 percent to obtain steel wires of 7 mm. diameter, and upsetting such wires so as to form an enlarged head thereon which has twice as large a diameter as that of the wire body portion. Such specimens were subjected to tension tests by gripping their head and body portions and the location of fracture was recorded. In the rectangular coordinate system shown, the ordinate represents the heating time in seconds and the abscissa the temperature in C. to which the wire stock is heated. The fractures occurring at a point on the wire stock is heated. The fractures occurring at a point on the wire body are each indicated in the graph by a small circle mark and those occurring at the neck portion ofthe wire by a cross mark (X).

It will readily be observed from the graphical illustration of H6. 1 that:

l The heating time has an upper limit for any heating temperature, inherent to the wire stock. If the wire is worked being heated for any period of time extending beyond such limit, reduction in strength of the upset portion results.

2. There is a definite relationship between the working temperature T, and the heating time, t. This relationship can be emperically approximated in the following manner. The curve P is selected so that only observed points representing working temperature and heating time combinations which do not result in fractures at the neck portion of the wire occur within the region below the curve. It will be seen from FIG. 1 that the curve P may be approximated by a hyperbolic curve Q. The curve 0 is represented by the general formula for a hyperbolic curve, that is,

)=B where T is the working temperature, t is the heating time, and a, 8, and B are constants. The lines T e: and t=8 represent the asymptotes of the curve Q. Since the heating time approaches zero as the working temperature is increased, 0 is asymptotic to the abscissa and 8=0. Q is thus represented by the equation (T) r--fl (A). The constants a and B can be determined by evaluating the equation at two observed points R and S at opposite ends of the observed range of temperatures and times on the curve O. From the observed data and points R2 T=540, F4 and S: #1200, r=0.8 represent the points closest to the upper limit P and at opposite extremes of the observed range. Evaluation of the equation at these points yields the values a=375 and B=660. Thus, the curve Q is represented by the equation (T-375)Xt=660, which is equivalent to From the above it will be seen that, for any given working temperature, T, uniform upsetting results can be obtained if the heating time, t, is not greater than the limit time t where t,.=660/ (T-375) According to the present invention, a rational upsetting method is provided upon the basis of such test results. With electric upsetters heretofore commonly used, supply and interruption of the working current have been effected upon the basis of the work size and in cases where the work is heated a particularly high temperature, it is supposed that the heating time generally exceeds the corresponding limit time t and this, causing the material of the wire portion being upset to soften, results in reduction in strength of the worked material. In contrast, according to the method of the invention, the work is rapidly formed by heating only for a short period of time t, which is less than the limit time t corresponding to the working temperature used, so that any adverse effect of high heat on the work strength can effectively be avoided.

Further advantages of the present method include, besides the improvement in product quality, improvement in working efficiency, reduced resistance to deformation enabling not only higher extents of deformation but also simplification and reduction in size of wire grip and pressing means compared with those used in conventional cold or hot wire working processes, and trim and satisfactory finish of the product.

Accordingly also to the present invention, there is provided an upsetting apparatus which is operable under conditions including a desired working rate and the corresponding safe working temperature as selected in the region in the T-t rectangular coordinate system lying beneath the limit curved, (T-aXt =B. To this end the inventive apparatus is featured with a variable transformer including notching means for adjusting the heating current and hence the working temperature T, a header assembly including a pressure regulator valve for adjusting the effective force of the piston thereby to control the working speed, and a timer for adjustment of the heating time t.

The heating time t and temperature T apparently should be selected relative to each other. With the inventive apparatus, the temperature T is adjusted principally by voltage regulation by means of the variable transformer while the heating time t is controlled principally by operating the pressure regulator valve to vary the pressure acting upon the piston in the header assembly thereby to adjust its working speed. Once the temperature T and time t are properly selected at a point in the region beneath the curve of limit t any lot of wire stock can be successively worked to obtain desired uniform products with a predetermined neck strength unless any variation in the working conditions, for example. a sudden change in room temperature effective to vary the cooling rate or a possible variation in electric resistance of the wire stock causing change in the heating efiect. occurs. It will be obvious that adjustment can also be made properly for such change in the working conditions.

it is to be understood that, where the wire stock to be worked varies in material, in diameter or in both. the specific constants. a and B. in the formula (A should be determined experimentally to obtain a corresponding limit curve, preliminarily to the adjustment of the machine to set the T and i values for the stock, conforming to the working conditions desired.

The timer included in the inventive apparatus for current supply and interruption is designed to function as follows:

1. Current supply in each cycle of upsetting operation is interrupted before the upsetting head reaches the end of its working stroke as any heating during the final portion of the stroke hardly makes any contribution to the result obtained.

2. The timer also serves the purpose of preventing overheating particularly when the voltage has been regulated to a particularly high value.

3. Use of the timer, made in a variable type, makes it easier to deal with different changes in working conditions.

Reference will next be made to FIG. 2, which illustrates one preferred embodiment of the invention, particularly showing its pneumatic system and electric circuitry.

In FIG. 2, the chuck 1 adapted to grip and hold a wire stock W is comprised ofa fixed member 3 and a movable member 2 both of steel and each having a toothed engaging surface 4 or 5 to grip and hold wire stock W firmly in place. The movable member 2 is actuated by a piston 6 with its rod 7. Copper electrodes 8 and 9 are fixed to movable and fixed chuck members 2 and 3 respectively, in an insulated relation thereto, and so arranged as to make contact with the wire stock W when it is "gri ped by the chuck 1. The fixed electrode 9 is grounded as mounted on the end of the rod 22 ofa piston 21 in an insulated relation thereof. As shown, the piston 21 is operably received in a separate pneumatic cylinder 23 and communicating with conduits 25 and 25a joined together by a solenoid valve 24. A finger 26 is carried on the piston rod 22 to serve the purpose of actuating a limit switch S The two solenoid valves 14 and 24 are also connected with conduits 28 and 29, respectively, which branch offa main airline 27 communicating with an appropriate air pressure source not shown. Pressure regulator valves 30 and 31 as well as pressure gauges 32 and 33 are attached to the branch conduits 28 and 29, respectively.

The pressure switch 8,, limit switch S and solenoids L, and L, of respective electromagnetic valves 14 and 24 are arranged in the circuit shown in FIG. 2, which is connected to an appropriate electric source and includes a foot-operated switch 5, and auxiliary relay R, a variable timer T, a magnet switch M and a variable transformer Tr.

The illustrated apparatus operates as follows:

l. When main or foot-operated switch S is depressed, the solenoid L, of electromagnetic valve 14 is energized to allow air pressure from branch conduit 28 to proceed through conduit 16 into the space in the cylinder 12 lying on one side of the piston 6 while communicating the cylinder space on the other side of the piston 6 with a discharge outlet through conduit 16a. Consequently, the piston 6 is forced downwards together with the moveable chuck member 2 so that the wire stock W to be worked is held in the chuck 1.

2. When the holding pressure of chuck 1 is built up to a predetermined level, the air pressure set in the c linder l2 and conduit 16 acts to close pressure valve 5, t ereby energizing timer T.

. The closing of pressure valve S, is also effective to close magnet switch M thereby to apply voltage to header electrode 20. The solenoid L, of electromagnetic valve 24 is also energized upon the closing of pressure valve S1 so that the valve 24 is operated so as to introduce air pressure from the branch conduit 29 into the right-hand side of the header cylinder 23 through conduit 25 while communicating the left-hand side of the cylinder 23 with a discharge outlet through conduit 25a. As the result, the upsetting head 20 carried on the end of the piston rod 22 is advanced leftwards to engage the adjacent end of wire stock W thereby to start current supply to the work and its deformation under compression.

4. Subsequently, as soon as the predetermined time previously set on the timer lapses, magnet switch M is opened to interrupt the current supply to the work whereas the header cylinder 23 remains activated to contribute leftward movement of header 20 and therefore deformation of work W.

. At the instant when the end of the wire stock W has been collapsed to form a rivet-headlike enlargement of a predetermined size, limit switch S is operated by the finger 26 carried by piston rod 22 and solenoid L is restored under the self-holding action of relay R whereby the piston 21 in the header cylinder 23 is moved back to its normal position. Then, foot-operated switch S is released to restore the solenoid L, whereby the piston 6 in chuck cylinder 12 is moved back to release the chuck 1 and the cycle of operation is completed.

For such cyclic operation, the working temperature is adjusted by notching the control arm 34 of transformer Tr to current. It is to be noted that, with the lever position properly selected, a heating time t which satisfies the relation t t where t, is the limit time satisfying the formula (A) for working temperature, can be obtained by manual or automatic setting of the timer T.

More than 5 seconds of heating time is not practical in practice of the invention for working efficiency in upsetting steel wires.

The test data set forth applies to steels containing from 0.80 to 0.95 percent C and from 0.6 to 0.9 percent Mg and specifically 0.80 percent C and 0.80 percent Mg to form a head of about twice the wire diameter.

The invention is not restricted to the features described above and shown in the drawing but may be varied in many ways within the scope of the appended claims.

What we claim is:

1. A method of upsetting steel wires to form enlarged heads thereon, characterized in that the wire stock is worked at conditions satisfying the formula LII t 660. T 375 wherein t, M Trepresents the working temperature in C.

2. A method of upsetting steel wires to form enlarged heads thereon, characterized in that the wire stock is worked at an elevated temperature satisfying the formula where t represents the heating time in seconds, T represents 7 the working temperature in degrees C., and a and 6 represent constants specific to the material and size of the wire stock and determined by tests of the wire stock and end points on a hyperbolic curved determined by such test data.

3. A method as in claim 1 including the step of using a steel wire stock having 0.80 to 0.095 percent C and 0.6 to 0.9 percent Mn therein 4. A method as in claim 2 including upsetting the wire end to form a head thereon of about twice the diameter of the processed steel wire.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 584, 188 Dated June 8, 1971 Invent0r(s) Chisato Okada and Yoshiaki Horiuchi It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Col. 2, line 8, (T X (t 5) should be (T o( x (t 6) Col. 2, line 14, "(T x t 5 AW should be (T -o X 1; =6 (A) Col. 2, line 56 "(T-qx t B should be (T a) x t fl C01. 4, line 55, Claim 1 after wherein t insert represents the heating time in seconds and Col. 4, line 56, Claim 1 Trepresents" should be T represents C01. 2, line 55, "curved" should be curve Signed and sealed this 28th day of March I 972.

( SEAL) Attest EDWARD M.FLETCHER, JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents FORM PO-105D (10- USCOMM-DC 60376-F69 US GOVERNMENT PRINTING OFFICE 969 O-3fi'33l 

2. A method of upsetting steel wires to form enlarged heads thereon, characterized in that the wire stock is worked at an elevated temperature satisfying the formula t Beta /(T- Alpha ), where t represents the heating time in seconds, T represents the working temperature in degrees C., and Alpha and Beta represent constants specific to the material and size of the wire stock and determined by tests of the wire stock and end points on a hyperbolic curved determined by such test data.
 3. A method as in claim 1 including the step of using a steel wire stock having 0.80 to 0.095 percent C and 0.6 to 0.9 percent Mn therein
 4. A method as in claim 2 including upsetting the wire end to form a head thereon of about twice the diameter of the processed steel wire. 